Stable lead alkyl compositions and a method for preparing the same



Unite-d States PatentiOfi ice 3,133,101 Patented May 12, 1964 3 133,101 STABLE LEAD ALKL COMPOSITIONS AND A METHGD FGR PREPARING THE SAME Wilford H. Thomas and Shirl E. Cook, Baton Rouge, La.,

assignors to Ethyl Corporation, New York, N.Y., a

corporation of Virginia No Drawing. Filed .lune 8, 1962, Ser. No. 200,939 9 Claims. (Cl. 260-437) This invention relates to alkyllead compositions which are stable at temperatures above 100 C. It also relates improved process for separating alkyllead compounds from the reaction products accompanying their synthesis. It is also applicable to a method for inhibiting thermal decomposition of an alkyllead product during its purification and blending with other products in making commercial antiknock fluids. It is applicable to minimizing the possibility of thermal decomposition during storage or transportation of an alkyllead product. It is especially applicable to preventing thermal decomposition of undiluted alkyllead compounds where the likelihood of .thermal decomposition is more of a problem.

As is Well known, tetraalkyllead antiknock compounds generally are produced by reacting a sodium-lead alloy with an alkyl halide. Due to recent marked improvements in the technology of alkyllead manufacture, thermal instability of alkyllead compounds during synthesis is no longer aproblem. However, the tetraalkyllead compound so produced is in admixture with various reaction byproducts from which it must be separated. Separation is effected by steam or vacuum distillation with subsequent purification of the tetraalkyllead distillate. Due

to the toxic and unstable nature of tetraalkyllead antiknock compounds, these distillation and purification operations are subject to many difiiculties. s

In these distillation and purification operations meticulous temperature control and exact safety measures are of paramount importance. The rate of decomposition of the alkyllead compound increases rapidly with small rises in temperature above the temperature where thermal decomposition becomes appreciable. For example, decomposition of tetraethyllead occurs at the rate of approximately 2 percent per hour at a temperature of 100 C., which is the customary temperature used in separating tetraethyllead from the reaction products accompanying its synthesis. At temperatures above 100 C., the decomposition rate increases logarithmically so that a point is soon reached Where external heat is no longer required and decomposition becomes selfpropagating.

Such likelihood of excessive decomposition is present also during blending handling, storage, and transportation. scavengers, gasoline or other materials, the alkyllead compound remains a concentrate and the problem of excessive thermal decomposition exists, even though the temperature is maintained normally Well below that of decomposition, For example, in the 'purification step wherein the tetraethyllead concentrateis washedjand blownWithair at atmospheric temperature.to'remove im purities, a sudden increase in temperaturemay' occur due occasionally freeze and the friction developed may cause a local overheating to a temperature above the temperature of decomposition of the tetraethyllead. Faulty Wiring, leaks onto steam pipes, and other accidental causes also may produce local overheatingwith resulting dangerous decomposition.

it is seen therefore that in those operations where an alkyllead compound is in the undiluted or concentrated stateviz., separation, purification, blending, transportation, and storagethe likelihood of excessive thermal decomposition must be provided for and effectively combatted.

An object of this invention is to stabilize alkyllead compounds against thermal decomposition during one or more of the following operations: 7 separation, purification, blending, transportation and storage.

The above and other objects of this invention are ac: complished by incorporating with alkyllead compounds a relatively small quantity of a mixturejof materials which has the property of synergistically inhibiting alkyllead thermal decomposition. The foregoing objects are also accomplished by conducting one' or more of the fore; going operations in the presence of such a mixture of materials. The mixtures which have been found to possess these unexpected properties are referred to hereinafter as thermal stabilizers.

The synergistic thermal stabilizer mixtures of this invention are composed of ethylene dibromide and trichloroethylene or tetrachloroethylene, or a mixture of these two last-named compounds. The concentrations in which they are used are equivalent to from about 0.05 to about 0.5 mole of ethylene dibromide'per mole of alkyllead compound, and from about 0.1 to about 30 percent or, more of the chloroethylenes, based on the weight of the alkyllead compound. These thermal sta bilizers when used in these amounts are'very efliective'in substantially retarding or preventing thermal decomposi tion of thealkyllead compound at temperatures ranging from about 100 C. up to about 195 C. for extended periods of time. Moreover, the behaviorfof thisj cfombination of additives in this regard is synergistic, i.e;, the thermal stabilization effectiveness of the whole is far greater than the sum' total of its parts. Such behavior is particularly pronounced at thepreferred concentrationsviz., from about 0.1 to about 0.4 mole of ethylene dibromide per mole of alkyllead compound, and from about 0.5 to about 20 percent of trichloroethylene or tetrachloroethylene, or both, based on the weight of the alkyllead compound.

The chief thermal decomposition products of alkyllead compounds are lead metal and, hydrocarbon gas.

Prior to; diluting the alkyllead concentrate with Hence, a very good index of alkyllead tion is liberation of this gas. 7

To illustrate the effectiveness of this invention, a series of direct comparisons weremade of the decomposition characteristics of unstabilized and stabilized tetraethyllead samples. A thermostatically controlled hot oil bath was fitted with a stirrer, thermometer, and a holder for a small reaction tube. A 100 cc. gas buret beside the bath, and equipped With a water-containing leveling bottle, was connected by means of rubber tubing with the reaction tube after the desired sample was introduced into this tube. After the bath was brought to a steadytempera ture 'of-195 C., the sample-containing tube was quickly thermal decomposiadjusted to hold the gas buret place-at a zer'o reading.

Then measured Wasthe timedufi'ng which the sample was to t he oxidation of triethylbismuth' whichis present as an impurity. Also, pumps used in handling tetraethyllead' held at 1 95 Cf without pronounced thermaldecomposition and' consequent gas evolution occurring. ,Thus, the longer the.

4 e; the me e l yj ta l was hs a k l lfiadcomposition. v

With pure tetraethyllead used in 1 ml. amounts, pro nounced thermal deterioration occurred almost immediately as evidenced by rapid gas evolution. In fact, the decomposition of unstabilized tetraethyllead will normally become uncontrollable if it is heated, whether rapidly or slowly, to even 130 C., unless it is possible to very rapidly cool it down to about 100 C. or below.

The remainder of the compositions tested in the manner described above and the results thereby obtained are shown in the following tables.

TABLE I Efiect of Additives on Thermal Decomposition of Alkyllead Compounds at 195 C.

J Thermal Ethylene Trichloro- Y Dibromide, Ethylene, g No. Mole/Mole Wt. Percent f TEL TEL minutes COMPOSITION or rnrs INVENTION COMPOSITIONS NOT or THIS INVENTION 0.10 nil 3 nil 15 1 TABLE II Ethylene Tetrachloro- Thermal Dibromide, Ethylene, Stability Mole/Mole Wt. Percent Timeto De- TEL TEL composition,

COMPOSITION OF THIS INVENTION COMPOSITIONS NOT OF THISINVENT ION 0. 05 nil 1 0. nu 3 nil 5 1 ml 1 tered, the addition of a small amount of thermal stabilizer mixture to the alkyllead compound will economically and satisfactorily eliminate most of the hazard involved.

While meticulous temperature control and exacting safety due to decomposition is considerably minimized through I the use of this invention.

This invention is useful in stabilizing alkyllead compounds in which at least one valence of the lead is satistied by an alkyl radical. For example, tetraethyllead, tetramethyllead, tetrapropyllead, dimethyldiethyllead, tri- It will be noted that the compositions of this invention exhibited a high degreeof synergistic effectiveness.

The above-described beneficial behavior of the thermal stabilizer mixtures of this invention also takes place with other alkyllead compounds such as triethyllead bromide and tetrapropyllead. In fact, these compounds when stabilized can be boiled and distilled at atmospheric pressure.

This invention is adapted to the stabilization of tetraethyllead and other alkyllead compounds at various stages after they have been formed and the diluents or excess allryl halide have been discharged from the autoclave. For example, one of the above thermal stabilizer combinations may be added in appropriate quantity to the alkyllead reaction concentrate just before the separation step which is conducted at a temperature close to the temperature where hazardous run-away decomposi- V ,0

tion is particularly prevalent. By adding oneof the above thermal stabilizer combinations to the reaction concentrate just prior to distillation, the danger arising 'from unexpected temperature increases is substantially elimi-' nated. i g

Most preferably, the. above thermal stabilizer combinations are employedto stabilize'the alkyllead compound both in storageand in shipping and especially to stabilize any alkyllead concentrate, i.e., compositionslcontaining at least percent by weight of alkyllead' compound. If elevated temperature conditions are likely to be encounethylphenyllead, and triethyllead bromide can be successporating therein a relatively small quantity of one of the thermal stabilizers of this invention. This invention is particularly well suited to the stabilization of any mixture involving two or more of the following compounds: tetramethyllead, ethyltrirnethyllead, diethyldirnethyllead, triethylmethyllead, and tetraethyllead.

While this invention has been discussed with reference to trichloroethylene' and tetrachloroethylene, it will be understood that other analogous compounds may be used in lieu thereof or in addition thereto.

What is claimed is:

1. A method of inhibiting the decomposition of an alkyllead compound at temperatures of from about C. to about C. which comprises incorporating with said compound from about 0.05 to about 0.5 mole of ethylene.

lected from the group consisting of trichloroethylene, tet

rachloroethylene, and mixtures thereof.

2. The method of claim 1 wherein the concentration of said ethylene dibromide is from about 0.1 to about 0.4 mole per mole of said compound, and wherein the concentrationof said chloroethylene is from about 0.5 to about 20 percent, based on the weight of said compound. T

3. In the process of producing an alkyllead compound by reacting a sodium lead, alloy'with alkyl chloride and separating the thus produced alkyllead compound from the reaction mass by steam distilaltion, the step which comprises conducting said steam distillation in the presence of from about 0.05 to about 0.5 mole of ethylene di bromide per mole of said compound, and from about 0.1 to about 30 percent of a chloroethylene, based onthe weight of saidcompoundysaid chloroethylene being se- I lected frorn the group consisting of trichloroethylene, tet-' rachloroethylene, and mixtures thereof. r

4. A concentrated alkyllead compound with which hasbeen blended from about 0.05 to about 0.5 mole of 6. The composition of clairn; 4 further characterizedin that the concentration of the ethylene dibromide ranges .frornabout 0.1 to about 0.4 mol'eper mole of said compound and in that the concentration of said chloroethylene rangesfromabout 0.5 to about 20 percent, based :on Y

the weight otsaid compound.

7. The composition 0i claim 6 wherein said compound is selected from the group "consisting oftetramethyllead,

'-;ethyltrimethyllead, diethyldimethyllead, tricthylnijethyh lead, tetraethyllead, and'mixtures thereofc 8'. The composition of claim 4'wherein the concentration of ethylene dibromide is about 0.1 mole per mole of alkyllead compound, and wherein said chloroethylene is trichloroethylene present in amount equivalent to about 15 percent based on the Weight of said alkyllead compound.

9. The composition of claim 4 wherein the concentration of ethylene dibrornide is about 0.05 mole per mole of alkyllead compound, and wherein said chloroethylene is tetrachloroethylene present in amount equivalent to about 5 percent based on the weight of said alkyllead compound.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A METHOD OF INHIBITING THE DECOMPOSITION OF AN ALKYLLEAD COMPOUND AT TEMPERATURES OF FROM ABOUT 100*C. TO ABOUT 195*C. WHICH COMPRISES INCORPORATING WITH SAID COMPOUND FROM ABOUT 0.05 TO ABOUT 0.5 MOLE OF ETHYLENE DIBROMIDE PER MOLE OF SAID COMPOUND, AND FROM ABOUT 0.1 TO ABOUT 30 PERCENT OF A CHLOROETHYLENE, BASED ON THE WEIGHT OF SAID COMPOUND, SAID CHLOROETHYLENE BEING SELECTED FROM THE GROUP CONSISTING OF TRICHLOROETHYLENE, TETRACHLOROETHYLENE, AND MIXTURES THEREOF. 